I really can't understand ________ her like that.

I really can't understand ________ her like that.
A、you treat
B、you to treat
C、why treat
D、you treating
【正确答案】：D
【题目解析】：understand 后面跟动词要求用动名词，答案D treating 前面加上you ，作逻辑主语用，也可以用your